The present invention is directed to a method of manufacturing diamond-impregnated drilling crowns for cylindrical diamond drilling tool bits.
Diamond-impregnated drilling crowns are generally fabricated as single-part annular cutting drills up to approximately 42 mm in diameter and are used for wet drilling. Over approximately 42 mm in diameter they are formed as annular segments and are used for both wet and dry drilling.
Up to the present time the annular segments have been fabricated individually and, in an additional step, they are placed on a hollow cylindrical carrier to form the drilling crowns. Such a method required high accuracy, and it is complicated and expensive. It must be noted that the quality of diamond-impregnated drilling crowns is determined by the size and shape of the segments, by the cross-section of the connection between the segment and the hollow cylindrical carrier, as well as by the accuracy and strength of the connection. The manufacture of curved segments involve costly waste or scraps.
For instance, a drilling crown is disclosed in U.S. Pat. No. 4,208,154 where the segments were placed on a hollow cylindrical carrier using an intermediate layer. To create an adequate or satisfactory connection between the segments and the hollow cylindrical carrier, the segment or the intermediate layer and the hollow cylindrical carrier must have a specifically configured connection area affording a positive interconnection of the parts. A positive connection partially compensates for a possibly inadequate connection between the segment and the hollow cylindrical carrier. However, this is obtained only at considerable cost, since segments for intermediate layers as well as the hollow cylindrical carrier are subjected to shaping processes involving increased fabrication costs.